1. Field of the Invention
The present invention is related to energy conversion devices and techniques, and, more particularly, is directed toward a method and apparatus for efficient conversion of thermal energy into mechanical energy.
2. Description of the Prior Art
Many practical embodiments of heat engines are known. Each, however, suffers from several deficiencies which reduce their efficiency or make them difficult and expensive to manufacture.
Generally, the flow of fluids in channels defined by solid walls becomes turbulent for large Reynold's numbers which results in a loss of energy via internal friction in the fluid. One example is pipes that conduct gas from the boiler to the engine, which pipes are necessitated by the physical separation of the two devices when a conventional water level boiler is used. Another example would be pumping losses that occur in a monotube boiler when such means are utilized to improve heat transfer from combustion gases to liquid in a small boiler. If a rotary boiler is used to improve heat transfer from combustion gases to the working fluid in a small boiler, both pipe losses and pumping losses occur. Another example occurs in conventional turbines, where the use of nozzles and impulse buckets results in much lossy turbulence. Further, losses occur in the stator channels of axial flow turbines.
A particular kind of rotary turbine known as the Tesla turbine employs a plurality of substantially planar, parallel discs between which fluid is directed. This turbine, invented by Nikola Tesla and described in his U.S. Pat. Nos. 1,061,142 and 1,061,206, has received some attention in the recent literature. See, for example: "An Analytical and Experimental Investigation of Multiple-Disk Turbines," W. Rice, Journal of Engineering for Power, Transactions of the ASME, January 1965, pages 29-36; "Investigation into the Performance Characteristics of a Friction Turbine," E. W. Beans, J. Spacecraft, Volume 3, No. 1, January 1966, pages 131-134; "Calculated Design Data for the Multiple-Disk Turbine Using Incompressible Fluid," M. J. Lawn, Jr. and W. Rice, Journal of Fluids Engineering, Transactions of the ASME, September 1974, pages 252-258; and "An Integral Solution for Compressible Flow Through Disc Turbines," C. E. Bassett, Jr., IECEC '75 Record, pages 1098-1106.
Unfortunately, the conventional Tesla turbine also suffers from turbulent losses which exist at both the input and output of the turbine due to the use of input nozzles and the spider-mounted shaft discs. There are also losses which results from "scrubbing" of the peripheral casing in both Tesla and conventional radial inflow turbines. End wall coupling to Tesla turbines is also a problem.
The high technology necessary to overcome the above-mentioned deficiencies in both conventional and Tesla turbines results in very expensive structures. For example, the pipes which conduct gas from the boiler to the engine must have smooth, uninterrupted interior surfaces to minimize losses, and must be thermally insulated. In a rotary boiler, there is a need for high temperature, high pressure rotary joints at the input and output. In an impulse bucket type of conventional turbine, the buckets must be shaped from refractory materials, and their attachment to the turbine wheel is difficult. Further, achievement of a low leakage fit between the rotor and stator is difficult in conventional turbines. In the Tesla turbine, the exhaust passages in the spider portion introduces weakness at the point of greatest stress, and upsets the flow at the greatest fluid/turbine relative velocity.
The foregoing deficiencies can be further appreciated if one considers the losses involved if one were to utilize a conventional rotary boiler to drive a conventional Tesla turbine. In such a system, a liquid is fed to the rotary boiler where heat is added. The kinetic energy of the liquid is raised by the rotary drive to the boiler and, after heat is added, the resultant gas spirals in toward a central exit pipe, gaining even more kinetic energy. A pipe connects the output from the boiler to the input of the Tesla turbine rotor. All of the kinetic energy thus generated in the boiler is now dissipated, and the turbulent flow of gas through the connecting pipe causes further losses. At the end of the connecting pipe, there is positioned a nozzle as the input conduit to the turbine whose purpose is to convert stagnation pressure into kinetic energy. The resultant gas jet, by scrubbing against the wall of the turbine casing and warming it considerably (resulting in further losses) travels a radial inward path through the discs of the conventional Tesla turbine. After considerable radial travel through these discs, a laminar flow condition exists and the kinetic energy of the gas begins to couple to the turbine rotor. At a further inward distance, laminar flow ceases, and further losses are incurred, until the exit holes or supporting spider structure are encountered, at which point turbulence becomes quite extreme, thereby warming the turbine shaft.
It may therefore be appreciated that considerable energy is lost in the conventional systems as set forth above, and it would be extremely desirable if a system for converting heat energy to mechanical energy could be devised which eliminates or substantially reduces such losses. It is toward achieving this end that the present invention is advanced.